US3463335A

US3463335A - Level-crowd control system for material handling loaders

Info

Publication number: US3463335A
Application number: US663815A
Authority: US
Inventors: Roy D Brownell; Granville Woolman
Original assignee: Baldwin Lima Hamilton Corp
Current assignee: Baldwin Lima Hamilton Corp
Priority date: 1967-08-28
Filing date: 1967-08-28
Publication date: 1969-08-26
Anticipated expiration: 1986-08-26

Description

Aug. 26, 1969 R. D- BROWNELL ET L 3,463,335

LEVEL-CROWD CONTROL SYSTEM FOR MATERIAL HANDLING LOADERS Filed Aug. 28, 1967 4 Sheets-$heet 1 frrafivim 4 Sheets-Sheet 2 l/MMM R. D. BROWNELL ET AL LEVEL-CROWD CONTROL SYSTEM FOR MATERIAL'HANDLING LOADERS Aug. 26, 1969 Filed Aug. 28, 1967 Aug. 26, 1969 BRQWNELL ET AL 3,463,335

LEVEL-CROWD CONTROL SYSTEM FOR MATERIAL HANDLING LOADERS Filed Aug. 28, 1967 4 Sheets-Sheet 3 m/z/iwrakr Pa a drawn/14 a gym/W115 yam/v4 w 1; 1w am frmimoy Aug. 26, 1969 R. D. BROWNELL ET AL 3,463,335

LEVEL-CROWD CONTROL SYSTEM FOR MATERIAL HANDLING LOADERS Filed Aug. 28, 1 967 4 Sheets-Sheet 4 f m Q Q iii W W Z WWW 6 mm W lax

United States Patent 3,463,335 LEVEL-CROWD CONTROL SYSTEM FOR MATERIAL HANDLING LOADERS Roy D. Brownell, Aurora, and Granville Woolman, Naperville, Ill., assignors to Baldwin-Lima-Hamilton Corporation, Chicago, 111., a corporation of Delaware Filed Aug. 28, 1967, Ser. No. 663,815

Int. Cl. E02f 3/00 US. Cl. 214-433 15 Claims ABSTRACT OF THE DISCLOSURE A control system for providing level-crowd operation for loaders of the type having an inner boom pivotally connected to the loader frame, an outer boom pivotally connected to the inner boom, a loader bucket pivotally connected to the outer boom, and separate hydraulic motors to pivot each of the booms and the loader bucket. To provide operator control over the extension and retraction of the loader bucket, the control system includes a single level-crowd control lever which is connected to operate a valve for actuation of the inner boom motor. In order to maintain the bucket pivot i.e., the pivotal connection between the loader bucket and the outer boom, along a predetermined level, the control system also includes detector means for sensing any departure of the bucket pivot from the level and an angle adjusting servo valve means operated by the detector means for actuating the outer boom motor so that the departure is eliminated. The operation of the angle adjusting valve may be effectuated by the detector means electrically, hydraulically, or mechanically. To enable the operator to change the elevation of the level along which the bucket pivot is maintained, the angle adjusting servo valve is also connected to be independently operated by an elevation control lever.

BACKGROUND OF THE INVENTION The present invention relates generally to material handling loaders and, more particularly, to automatic control systems for loaders having pivotally interconnected inner and outer booms and a loader bucket pivotally connected to the outer boom.

With such loaders, it is often desirable to extend or crowd the loader bucket substantially horizontally into the material being loaded, an action commonly referred to as level-crowding. As a general rule, this requires that provision be made to maintain the point of pivotal connection between the loader bucket and the outer boom along a predetermined level.

In the past, this has been done by providing the outer boom with a rigid extension projecting above the pivotal connection of the inner and outer booms. A link is then connected between a point on the loader frame and the upper end of the extension. With this arrangement, level-crowding action is approximated since the link forcibly swings the outer boom in a manner to maintain the bucket pivot along a predetermined level as the inner boom is swung. Additionally provision has been made to vary the length of the link to permit the elevation of the level along which the bucket pivot is maintained to be changed. However, this construction is not entirely satisfactory since the weight of the necessarily heavy extension and link must be supported at least in significant part by the inner boom thus causing a corresponding reduction in the payload capacity of the loader.

Another method which has been employed involves the use of separate control levers which are simultaneously operated for simultaneous actuation of the inner and outer boom motors. This eliminates the need for the heavy linkage, but has the disadvantage of requiring considerable operator skill to obtain the particular simultaneous actuation of the motors necessary for levelcrowding.

SUMMARY OF THE INVENTION It is a primary aim of this invention to provide, for a material handling loader of the above-described type, a control system which permits the loader to be operated in a level-crowd manner under the control of a single control lever and, yet, which does not materially reduce the payload capacity of the loader. A more specific object is to provide a control system of the foregoing type for automatically maintaining the bucket pivot along a predetermined level. A related detailed object is the provision of a control system wherein a hydraulic motor, which is connected to pivot the outer boom, is actuated in response to a departure of the bucket pivot from a predetermined level to return the bucket pivot to that level.

Another object of the present invention is to provide in a control system of the foregoing type, an elevation control means to enable the operator to select the elevation of the level along which the bucket pivot is maintained. One feature of the present invention is the provision of a level-crowd system with an elevation control means which requires a minimum of operator attention to change the elevation of the level along which the bucket pivot is maintained.

A further object of this invention is to provide a lightweight level-crowd control system which is simple and reliable and which requires relatively little operator skill. It is also an object to provide a level-crowd control system of the foregoing type which may be readily installed on new or existing level-crowd type loaders of a wide variety of sizes and designs.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will be apparent upon reading the following detailed description with reference to the attached drawings, in which:

FIG. 1 is a side elevation of a bucket type loader with dot-dash lines illustrating the bucket and outer boom extended in a level-crowd manner from their solid line positions;

FIG. 2 is an enlarged fragmentary schematic of one embodiment of a level-crowd control system for a bucket type loader such as shown in FIG. 1 wherein the angle adjusting servovalve is mechanically operated;

FIG. 2a is a further enlarged view, partly in section, of a portion of the control system of FIG. 2, and illustrates an arrangement which permits the operator to rapidly change the bucket elevation control lever setting.

FIG. 3 is an enlarged fragmentary schematic of another embodiment of a level-crowd control system wherein the angle adjusting servo valve is hydraulically operated;

FIG. 3a is a further enlarged view, partly in section, of a portion of the control system of FIG. 3, and illustrates an arrangement which permits the operator to rapidly change the bucket elevation control lever setting; and

FIG. 4 is an enlarged fragmentary schematic of still another embodiment of the level-crowd control system of the present invention wherein the angle adjusting servovalve is electrohydraulically operated.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS While the invention will be described in connection with particular embodiments, it will be understood that the intent is not to limit it to those embodiments. To the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Turning now to the drawings and particularly to FIGS. 1 and 2, there is shown a bucket type loader indicated generally at 10. As illustrated here, the loader is supported by ground engaging tracks 11 and is provided with a turntable structure 12 which carries the loader frame 13 and which permits rotation of the frame 13 in either direction about the turnable vertical axis. Mounted on the frame 13 there is a cab 14 in which the controls for operating the loader are located and which encloses the motor (not shown) for driving the tracks 11. Of course, it will be understood that the present invention is not limited to track-laying type loaders and that it is equally applicable to others, such as wheeled types.

The loader includes an inner boom 15 pivotally mounted at 16 on the forward portion of the frame 13, an outer boom 17 pivotally mounted at 18 adjacent the upper end of the inner boom 15, and a loader bucket 19 pivotally mounted at 20 adjacent the outer end of the outer boom 17. While the inner and outer booms 15, 17 are both described and illustrated herein in the singular, it will be appreciated that the present invention may be practiced with the respective pairs of laterally spaced inner and outer booms.

For swinging the inner boom 15, the outer boom 17, and the bucket 19 about their respective

horizontal pivots

16, 18, and 20, separate power units are provided. As shown, each of the power units 2123 is preferably a hydraulic motor of the cylinder and piston type and, in the illustrated embodiments, each of the cylinders is double acting.

To effectuate level-crowding action, the inner boom 15 is swung about its pivot 16 to extend and retract the bucket 19, the outer boom 17 is swung about its pivot 18 to maintain the bucket pivot 20 substantially at a preselected level, and the bucket 19 is swung about its pivot 20 to maintain a fixed, level relationship with the ground. To this end, the inner boom motor 21 has its cylinder pivotally connected at 24 to an anchor plate 25 which is rigidly secured to the frame 13, and its piston rod pivotally connected adjacent the upper end of the inner boom 15, in this instance to the inner-outer boom pivot 18. The outer boom motor 22 has its cylinder pivotally connected at 26 intermediate the ends of the inner boom 15, and its piston rod pivotally connected at 27 intermediate the ends of the outer boom 17. The bucket motor 23 has its cylinder pivotally connected at 28 to a lever arm 29, and its piston rod pivotally connected at 30 to the bucket 19 with the pivot 30 being spaced sufficiently from the bucket pivot 20 to provide a suitable lever arm therebetween. The lever arm 29 has one end pivotally connected at 31 to the outer boom 17 and its other end pivotally connected at 32 to one end of a parallelogram link 33. The other end of the parallelogram link 33 is pivotally connected at 34 to the outer end of the inner boom 15.

The bucket motor 23 is preferably automatically actuated through the operation of a control system (not shown) to maintain the bucket 19 in a fixed angular relationship relative to the ground as the inner and outer booms are swung. However, this control system for providing automatic leveling of the bucket 19 forms no part of the present invention. Therefore, since various embodiments of such a control system are disclosed in detail in the copending application Ser. No. 776,350, entitled Automatic Bucket Tilt Control, and assigned to the same assignee as this application, reference is made to that copending application for a full description of the actuating mechanism for the bucket motor 23.

In order to provide controlled actuation of the inner boom motor 21 to pivot the inner boom 15 with respect to the frame 13 so as to extend and retract the loader bucket 19, pressure fluid is provided from a reservoir 41 by a pump 42, and the application of this pressure fluid to the opposite ends of the motor 21 is under the control of the operator. To this end, a four-way valve 43 is connected to selectively couple the rod end and head end input lines, 44 and 45, respectively, of the motor 21 to a supply line 45, which is provided with pressure fluid by the pump 42, and to a return line 47, which is connected to drain to the reservoir 41. Operator control of the valve 43 is provided by a control lever 48 which is coupled to the valve spool 49 through a mechanical linkage 50. Thus, to extend the bucket 19, the operator moves the control lever 43 in one direction to shift the valve spool 49 so that the head end input line 45 is pressurized causing extension of the piston rod of the inner boom motor 21. Conversely, movement of the control lever 48 in the other direction causes pressurization of the rod end input line 44 and consequent retraction of the loader bucket 19.

In accordance with the present invention, to provide automatic level-crowd operation of the inner and outer booms, provision is made to automatically swing the outer boom 17 to maintain the bucket pivot 20 along a predetermined level as the inner boom 15 is swung. Toward this end, a detector means is provided for sensing any departure of the bucket pivot 20 from the predetermined level, and an angle adjusting means is operated by the detector means for automatically actuating the outer boom motor 22 so that the bucket pivot 20 is returned to the predetermined level.

In carrying out the invention, the detector means includes a detecting link connected between a point that moves with the outer boom 17, a point referred to herein for convenience as the outer boom poin and a reference point. The outer boom point is chosen to be a point which follows an arc of constant radius about the reference point during level movement of the bucket pivot 20, and the detecting link is selected to have a length defining this radius. As will become apparent, the reference point may be either fixed or floating, and the detecting link may be a fixed or variable length.

In the embodiment of FIG. 2, where the angle adjusting means is mechanically operated by the detector means, such as the mechanical linkage indicated generally at 51, so that the motion of the reference point resulting from a departure of the bucket pivot 20 from the predetermined level may be employed to operate the angle adjusting means. As can be seen, the linkage 51 includes a rod 52 which has its upper end pivotally connected at 53 to an extension arm 54, and its lower end, in this instance, pivotally connected at 56 to one end of an operating link 57. The other end of the operating link 57 is pivotally connected at 58 to both a plate 59 and the loader frame 13.

The pivot pin 53 serves as the outer boom point, and the pivot 56 provides the floating reference point about which the pivot 53 follows an arc of constant radius during level movement of the bucket pivot 20. For this reason, the extension arm 54 is rigid with the outer boom and extends therefrom at an angle to the rear of the axis passing through the

pivots

18 and 20, and the rod 52, which serves as the detecting link, has a fixed length defining the radius of the are followed by the pivot 53 for level movement of the bucket pivot 20. As a result, if the bucket pivot rises above the predetermined level, the operating link 57 is rocked downwardly about the pivot 58 and, conversely, if the bucket pivot 20 falls below the predetermined level, the link 57 is rocked upwardly.

To automatically actuate the outer boom motor 22 in response to a detected departure of the bucket pivot 20 from the predetermined level, the angle adjusting means includes a four-way valve 61 connected for selectively supplying and draining pressure fluid to and from the opposite ends of the outer boom motor 22 in response to the rocking of the link 57. To this end, the spool 62 of the valve 61 is connected to the link 57 intermediate the pivots 56 and 58 so that the valve 61 is operated by the rocking of the link 57 to selectively couple the head end input line 63 and the rod end input line 64 to a respective one of a supply line 65 and a return line 66. The supply line 65 is supplied with pressure fluid from the reservoir 41 by a pump 67 while the return line 66 is connected to drain to the reservoir 41. The operation of the valve 61 depends on the direction in which the link 57 is rocked. For example, when the link 57 is rocked downwardly, the valve spool 62 is shifted so that the valve 61 is operated to couple the head end input line 63 to the return line 66 and the rod end input line to the supply line 65. Conversely, if the link 57 is rocked upwardly, the valve 61 is operated to connect the head end input line 63 to the supply line 65 and the rod end input line 64 to the return line 66.

Of course, it will be understood that the valve 61 may be operated in a variety of different ways. For example, in contrast to the manner illustrated, the valve may be equally as well connected in the detecting link 52 between the pivots 53 and 56 for operation by the linear motion of the detecting link itself.

As another feature of the present invention, an elevational control means is provided to permit the operator to change the elevation of the level along which the bucket pivot 20 is maintained. For this reason, in the embodiment of FIG. 2, a control lever 70 is provided to enable the operator to rock the body of the valve 61 either upwardly or downwardly. This results in :a shifting of the reference point 56 since the valve 61 is operated to actuate the outer boom motor 22 until the rod 52 shifts the reference point 56 to return the valve spool 62 to a neutral position. By shifting the reference point 56, the level along which the bucket pivot 20 is maintained may be either raised or lowered. As illustrated, the control lever 70 is pivotally connected intermediate its ends at 71 to a fixed point, typically to the frame 13. The lower end of the control lever 70 is rigidly fixed to one end of an arm 72, the other end of which is pivotally connected at 73 to the upper end of a motion transmitting link indicated generally at 74. The lower end of the link 74 is pivotally connected at 75 to the plate 59 which, in turn, is rigidly connected to the body of the valve 61. Consequently, movement of the control lever 70 to the right causes the body of the valve 61 to rock downwardly about the pivot 58 so that the outer boom motor 22 is actuated to raise the bucket pivot 20. On the other hand, movement of the control lever 70 to the left rocks the body of the valve 61 upwardly so that the outer boom 22 is actuated to lower the bucket pivot 20.

In carrying out this feature of the invention the motion transmitting link 74 may advantageously include a bias means which is activated by movement of the control lever 70 so that the operator may rapidly move the control lever 70 to a position corresponding to a newly selected elevation for the bucket pivot 20 and be assured that the outer boom motor 22 will be actuated to bring the bucket pivot 20 to that elevation without further op erator attention. As best shown in FIG. 2a, the bias means may be a spring loaded plunger assembly generally indicated at 76. The plunger assembly 76 includes a compression spring 77 which is held between a pair of locating washers or collars 78 and 79. The locating collars 78 and 79 are fixed at spaced points on the upper end of a plunger 80 and are held within a housing 81 by the annular shoulders 82a and 82b, respectively, provided by the housing. In this instance the plunger assembly 76 is coextensive with the transmitting link 74 and, therefore, the housing 81 is connected to the operating lever 70 through the pivot 73 while the lower end of the plunger 80 is pivotally connected at 75 to the plate 59. Thus, movement of the lever 70 in either direction serves to compress the spring 77 to create a biasing force which is applied to the plate 59 thereby assuring that the outer boom motor 22 will be actuated until the bucket pivot 20 has assumed the elevation corresponding to the position of the control lever 70. Of course, it will be appreciated that the bias means may equally as well form only a part of the motion transmitting link 74.

Turning now to FIGS. 3 and So, there is illustrated a modified embodiment of the present invention comprising a hydraulic system interconnecting the outer boom 17 and the boom elevation control lever 70 for operating a pilot-type outer boom angle adjusting valve 83. It will be noted that the remainder of the control system is the same as previously described with reference to FIGS. 1 and 2 and has, therefore, been identified by similar reference numerals.

In this embodiment, the detector means may advantageously be of the fixed reference point type with a variable length detecting link, indicated generally at 84, having its lower end pivotally connected at to a fixed reference point, typically a point on the loader frame 13, and its upper end pivotally connected at 53 to the extension arm 54. The pivot 53 serves as the outer boom point in the same manner as previously described with reference to FIG. 2. Therefore, the length of the link 84 changes in response to a departure of the bucket pivot 20 from the predetermined level.

The major advantage of employing this type detector in this embodiment is that the variations in the length of the detecting link 84 may be readily employed to create the pressure differential across the pilot section of the valve 83 necessary to operate the valve. As illustrated, the detecting link 84 includes a double acting, hydraulic cylinder 86, a piston 87 slidable within the cylinder 86, and a piston rod 88 fixed to the piston 87 and extending from the cylinder 86 in the usual manner. To simplify the system, the cylinder 86 is preferably of the balanced displacement type.

For providing a pressure differential in response to a departure of the bucket pivot 20 from the predetermined level, the cylinder 86 and the piston rod. 88 are connected between the outer boom point 53 and the reference point 85 so that the piston 87 is shifted in response to such a departure. To apply this pressure difierential across the pilot section of the valve 83 to operate the valve for actuation of the outer boom motor 22 to return the bucket pivot 20 to the predetermined level, the head end and rod end of the cylinder 86 are hydraulically connected across the pilot section of the valve 83 by the

pilot lines

89 and 90, respectively.

The elevation of the level along which the bucket pivot 20 is maintained is established by the length of the detecting link 84 under quiescent conditions which, in turn, is determined by the position of the piston 87 under such conditions. Therefore, to establish the level along which the bucket pivot 20 is maintained, the elevation control means for this embodiment includes a reference means for providing a reference pressure differential across the pilot section of the valve 83. In this manner, the piston 87 is required to assume a particular position within the cylinder 86 so that the pressure differential provided across the pilot section of the valve 83 by the cylinder 86 balances out the pressure differential provided by the reference means. Conveniently, the reference means may be a double-acting hydraulic cylinder 91 with its head end and rod end hydraulically connected across the pilot section of the valve 83 by the

pilot lines

89 and 90 so that the reference pressure differential is determined by the position of a piston 92. Preferably, the cylinder 91 is of the balanced displacement type.

To enable the operator to change the elevation of the level along which the bucket pivot is 'maintained, means are provided by the elevation control means to enable the operator to change the reference pressure differential applied across the pilot section of the valve 83. Accordingly, the cylinder 91 is pivotally connected at 93 to a fixed point, such as a point on the frame 13, and the piston 92 is fixed to a piston rod 94 which, in turn, is pivotally connected at 95 to the lower end of the elevation control lever 70. In this instance, the head and rod ends of the cylinder 86 are hydraulically interconnected with the rod and head ends, respectively, of the cylinder 91 by the

pilot lines

89 and 90, respectively. Consequently, movement of the control lever to the right increases the elevation of the level along which the bucket pivot 20 is maintained while movement of the control lever to the left decreases the elevation of such level.

Desirably, the connection between the control lever 70 and the piston 92 includes a bias means, such as the spring loaded plunger assembly 76 previously described with reference to FIGS. 2 and 2a, so that the operator may rapidly move the control lever 70 to a position corresponding to a particular elevation of the bucket pivot 20 and be assured that the bucket motor 22 will be actuated until the bucket pivot 20 reaches the newly selected elevation. For this reason, as illustrated, the piston rod 94 is connected as the plunger of the plunger assembly 76, and the housing 81 of the plunger assembly 76 is pivotally connected at 95 to the lower end of the control lever 70.

From the foregoing, it will be appreciated that use of balanced displacement type cylinders for the cylinders 86 and 91 provides a quick and uniform response for the pilot operated embodiment of FIG. 3. However, it will be apparent that other types of double-acting cylinders could be readily employed.

Another embodiment of the control system is shown in FIG. 4 to be an electro-hydraulic, pilot operated system. Various features of this embodiment are the same as previously described with reference to FIGS. 2 and 3 and, therefore, the same reference numerals as used in FIGS. 2 and 3 have been used in FIG. 4 to identify these features.

As in the embodiment of FIGS. 2 and 2a, in this embodiment it is convenient to employ a floating reference point type detector means. In this case, the detector means includes a mechanical linkage, indicated generally at 101, which extends between the frame 13 and the outer boom 17 to sense changes in the elevation of the bucket pivot 20. The linkage 101 includes a rod 102 which has its upper end pivotally connected at 53 to the extension arm 54 and its lower end pivotally connected at 103 to one end of an arm 104. The other end of the arm 104 is pivotally connected at 105 to the frame 13. The length of the rod 102 is chosen to define the radius of the arc about the pivot 103 so that the pivot must follow if the bucket pivot 20 is to be maintained along a horizontal level. Consequently, changes in the elevation of the bucket pivot 20 result in rocking of the arm 104 about the pivot 105.

In this embodiment the angle adjusting means are electrically responsive to the detector means. For this reason, variable voltage means are operated by the mechanical linkage 101 to indicate detected departures of the bucket pivot 20 from the predetermined level. As illustrated, the detector means inlcudes a potentiometer 106 which is connected across a supply source, such as a battery 107. Preferably, the potentiometer 106 is of the rotary type and is fixed to the frame 13, and the pivot 105 is located at the center of the potentiometer 106 and the slider 108 of the potentiometer 106 is carried by the arm 104 for rotation about the pivot 105. Consequently, the rocking of the arm 104 which accompanies a departure of the bucket pivot 20 from the preselected level results in a change in 8 the voltage drop between the slider 108 and a reference lead 109.

The elevation control means in the embodiment of FIG. 4 includes means for supplying a reference voltage having a magnitude corresponding to the desired elevation of the bucket pivot 20. Accordingly, there is provided a potentiometer 110 which is connected across the battery 107 and which has a slider 111. The reference voltage is the voltage between the slider 111 and the reference lead 109.

To enable the operator to change the elevation of the horizontal level along which the bucket pivot 20 is maintained the elevation control means includes means to enable the operator to change the magnitude of the reference voltage. In the illustrated embodiment, where the potentiometer 110 is of the rotary type, the elevation control lever 70 is pivotally connected at 112 at the center of the potentiometer 110 and the slider 111 is carried by the control lever 70 for rotation about the pivot 112. The movement of the control lever 70 to change the elevation of the bucket pivot 20 may be as rapid as desired.

The angle adjusting function in the embodiment of FIG. 4 is performed electro-hydraulically so that the outer boom motor 22 is actuated to eliminate any existing imbalance between the variable voltage supplied by the detecting means and the reference voltage provided by the elevation control means. An electrically operated pilot valve 119 with a control coil 113 is shown connected between the sliders 108 and 111. The pilot valve 119 is operated by current flow through the control coil 113 and is responsive to the direction of this current flow to connect a selected one of the pilot lines 117 and 118 to a supply line 114 and the other of the pilot lines to a drain line 115. The supply line 114 is provided with pressure fluid from the reservoir 41 by a pump 116 While the drain line is returned to the reservoir 41 typically through the return line 66. In the absence of current flow through the control coil 113, the pilot valve 119 operates to connect the supply line 114 to the drain line 115.

The sensitivity of the pilot valve 119 to the direction of the current flow through the control coil 113 insures that the pilot valve 119 will operate to create a pressure differential between the pilot lines 117 and 118 which is in the direction necessary for operation of the valve 83 to actuate the outer boom motor 22 in a direction to eliminate the imbalance between the voltage provided by the detecting means and the reference voltage provided by the control means. For example, assuming that the bucket pivot 20 falls below the horizontal level corresponding to the setting of the control lever 70, the slider 108 of the detecting means potentiometer 106 is moved to the left to increase the voltage at the left-hand end of the control coil 113. The resulting current flow through the coil 113 operates the pilot valve 119 to couple the pilot line 89 to the supply line 114 and the pilot line 90 to the drain line 115. As a result, the outer boom motor 22 is actuated to swing the outer boom 17 outwardly thereby raising the bucket pivot 20 until the voltages at the opposite ends of the coil 113 are again equal.

From the foregoing, it will be appreciated that each of the illustrated embodiments provides detector means for sensing any departures of the bucket pivot 20 from a predetermined horizontal level and angle adjusting means which are responsive to the detector means to eliminate any such departures. Further, it will be seen that in each of the embodiments elevation control means are provided to enable the operator to change the elevation of the level at which the bucket pivot is maintained. Finally, the elevation control means provided are such that the operator time consumed in operating them is minimized.

We claim as our invention:

1. A control system for a material handling loader having a frame, an inner boom pivotally mounted on the frame, an outer boom pivotally mounted on the inner boom, a loader bucket, and pivot means for pivotally mounting said bucket on said outer boom, said system comprising the combination of power means for pivoting said outer boom with respect to said inner boom, detector means for sensing departures of said bucket pivot means from a selected height incident to pivotal movements of said inner boom, and outer boom angle adjusting means coupled to said detector means for actuating said power means in response to sensing said departures to return said bucket pivot means to said selected height.

2. A control system as defined in claim 1 wherein said power means is hydraulically actuated and said outer boom angle adjusting means includes a valve operable by said detector means for controlling the supply and discharge of fluid to and from said power means.

3. A control system as defined in claim 2 wherein said detector means includes a detecting link pivotally connected at one end to a point on the outer boom and at its other end to a reference point, said point on the outer boom being selected to be a point which follows an arc of constant radius about said reference point during horizontal movement of said bucket pivot, and said detecting link having a length defining said radius.

4. A control system as defined in claim 2 further including a manually operable elevation control means connected for independently operating said valve to thereby enable a new elevation for said selected level to be chosen.

5. A control system as defined in claim 4 wherein said elevation control means includes a bias means for permitting said elevation control means to be rapidly operated, said bias means being connected to store a biasing force upon rapid operation of said elevation control means and to apply this biasing force for operating said valve until said pivot means reaches said new elevation.

6. A control system as defined in claim 3 wherein said reference point is floating, said valve includes a valve body and a valve spool, and said detector means further includes an operating link having one end pivotally connected to said detecting link at said reference point and an opposite end pivotally connected to said frame, one of said valve body and valve spool being connected to said operating link intermediate said ends whereby the rocking of said operating link incident to a departure of said pivot means from said selected level provides relative movement between said valve body and valve spool to thereby operate said valve.

7. A control system as defined in claim 6 further including an elevation control means for permitting a new elevation for said selected level to be chosen, said elevation control means including a manually operable control lever and a linkage connected between said control lever and the other of said valve body and valve spool for providing relative movement between said valve body and valve spool in response to movement of said control lever to thereby operate said valve until said pivot means reaches said new elevation.

8. A control system as defined in claim 7 wherein said linkage includes a bias means for permitting rapid movement of said control lever to a position corresponding to said new elevation and actuation of said power means until said pivot means reaches said new elevation, said bias means including a spring connected between said control lever and said other of said valve body and valve spool for storing a biasing force upon movement of said control lever and for applying this biasing force to operate said valve until said pivot means reaches said new elevation.

9. A control system as defined in claim 3 wherein said reference point is a fixed point on said frame, said valve has a pair of pilot ports and is operated when a pressure differential exists across these pilot ports, and said detecting link includes a first double acting hydraulic cylinder having a port at each of its opposite ends and a first piston slidable within said first cylinder, said ports of said first cylinder each being connected to a respective one of said pilot ports, said first cylinder and said first piston each being pivotally connected to a respective one of said point on said outer boom and said reference point whereby said first piston is shifted relative to said first cylinder upon a departure of said pivot means from said selected level to thereby provide a pressure differential across said pilot ports for operating said valve.

10. A control system as defined in claim 9 further comprising an elevation control means for permitting a new elevation for said selected level to be chosen, said elevation control means including a manually operable control lever, a second double acting hydraulic cylinder having a port at each of its opposite ends hydraulically connected to a respective one of said pilot ports, a second piston slidable within said second cylinder, and a linkage for connecting said control lever to one of said second cylinder and second piston, the other of said second cylinder and second piston being connected to a stationary point whereby movement of said control lever to a position corresponding to said new elevation creates a pressure differential between said pilot ports for operating said valve until said pivot means reaches said new elevation.

11. A control system as defined in claim 10 wherein said first and second cylinders are balanced displacement type cylinders, and said linkage includes a bias means for permitting rapid movement of said control lever to a position corresponding to said new elevation and actuation of said power means until said pivot means reaches said new elevation, said bias means including a spring connected between said control lever and said one of said second cylinder and second piston for storing a biasing force upon movement of said control lever and for applying this biasing force to operate said valve until said pivot means reaches said new elevation.

12. A control system as defined in claim 2 wherein said valve is a pilot operated valve having a pair of pilot ports and being operated when a pressure differential exists across these pilot ports, said angle adjusting means further includes an electrically operated pilot valve having a pair of output ports each hydraulically connected to a respective one of said pilot ports and an electrical control element responsive to a current flow therethrough to create a pressure differential between said output ports to thereby operate said pilot operated valve, and said detector means includes variable voltage means coupled across said control element and operated in response to a departure of said pivot means from said selected level to provide a current flow through said control element.

13. A control system as defined in claim 12 further comprising an elevation control means. for permitting a new elevation for said selected level to be chosen, said elevation control means including a reference voltage means coupled for applying a reference voltage across said control element and a manually operable control lever connected to said reference voltage means whereby said reference voltage is varied upon movement of said control lever to a position corresponding to said new elevation to thereby provide current flow through said control element until said pivot means reaches said new elevation.

14. A control system as defined in claim 13 wherein said reference point is floating, said detector means further includes a link with one end pivotally connected to said detecting link at said reference point and an opposite end pivotally connected to said frame, and said variable voltage means includes a first potentiometer mounted on said frame concentrically with the pivotal connection of said opposite end of said link and a first slider rigidly fixed to said opposite end of said detecting link whereby said first slider is moved on said first potentiometer in response to a change in the elevation of said pivot means,

said control element being connected between one end of said first potentiometer and said first slider whereby a current flow is provided through said control element in response to a departure of said pivot means from said selected level.

15. A control system as defined in claim 14 wherein said control lever has a pivot point and said elevation control means further includes a second rotary poten- 5 tiometer mounted concentrically with said pivot point and a second slider rigidly fixed to said control lever at said pivot point whereby said second slider is moved on said second potentiometer in response to movement of said control lever, said control element being connected between one end of said second potentiometer and said second slider whereby, when said control lever is moved to a position corresponding to a new elevation, a current fiow is provided through said control element until said pivot means reaches said new elevation.

References Cited UNITED STATES PATENTS 3,343,693 9/1967 Becker 2l4138 GERALD M. FORLENZA, Primary Examiner 10 H. O. SCHULZ, Assistant Examiner U.S. Cl. X.R. 214-762